[PATCH 1/4] for 2.6.18, revert "Drop tasklist lock in do_sched_setscheduler"

[Oleg Nesterov <oleg@tv-sign.ru>]

sched_setscheduler() looks at ->signal->rlim[]. It is unsafe do dereference
->signal unless tasklist_lock or ->siglock is held (or p == current). We pin
the task structure, but this can't prevent from release_task()->__exit_signal()
which sets ->signal = NULL.

Restore tasklist_lock across the setscheduler call.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.18-rc4/kernel/sched.c~1_revert	2006-08-19 17:50:56.000000000 +0400
+++ 2.6.18-rc4/kernel/sched.c	2006-08-19 18:15:15.000000000 +0400
@@ -4162,10 +4162,8 @@ do_sched_setscheduler(pid_t pid, int pol
 		read_unlock_irq(&tasklist_lock);
 		return -ESRCH;
 	}
-	get_task_struct(p);
-	read_unlock_irq(&tasklist_lock);
 	retval = sched_setscheduler(p, policy, &lparam);
-	put_task_struct(p);
+	read_unlock_irq(&tasklist_lock);
 
 	return retval;
 }

-
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